Preparation of 3,5-disubstituted-4-acetoxystyrene

ABSTRACT

3-substituted-4-hydroxy- and 4-acetoxystyrene compounds, especially 3,5-di(methyl, bromo or chloro)-4-acetoxystyrene as well as a process for its preparation. 2,6-dimethylphenol is acylated with acetic anhydride and HF catalyzed to produce 3,5-dimethyl-4-hydroxy-acetophenone. After subsequent esterification with acetic anhydride and catalyzed hydrogenation to form 1-(3&#39;,5&#39;-dimethyl-4&#39;-acetoxyphenyl)ethanol, this intermediate is then dehydrated with an acid and a polymerization inhibitor to produce 3,5-dimethyl-4-acetoxystyrene.

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/097,809, filed Sept. 16, 1987, now abandoned which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to 3-substituted-4-hydroxy- and4-acetoxystyrene compounds and more particularly to3,5-disubstituted-4-acetoxystyrene wherein the 3,5-substitution isindependently C₁ to C₁₀ alkyl or alkoxy, amino, such as primary orsecondary amino or halo, and a process for its preparation. In its mostpreferred form, the invention relates to 3-mono- and 3,5-dihalogenated4-acetoxystyrenes which contain chlorine or bromine as the halogen, anda method of preparation thereof.

3,5-dibromo-4-hydroxystyrene compounds have been known for a long timeand were initially prepared from 4-hydroxycinnamic acid by

(a) bromination of positions 3 and 5 on the ring as well as addition ofbromine to the double bond.

(b) dehydrobromination with concurrent decarboxylation, leading toreconstitution of the vinylic double bond.

(c) then, addition of hydrogen bromide to said double bond to form asaturated vicinal dibromide,

(d) finally, by debromination for reconstruction of the vinylic doublebond (see Liebigs Annalen der Chemie, 322, 235 (1902)) as shown in thefollowing scheme: ##STR1## It is known in the art to produce monomers,homopolymers and copolymers of unsubstituted 4-acetoxystyrene and tohydrolyze the same to produce 4-hydroxystyrene derivatives or polyvinylphenols. Such find use in the production of photoresists, adhesives,coating compositions, and the like. In particular, polymers orcopolymers prepared from non-halogenated monomers are used for preparingcoating compositions and as binders for photoresists. In thisconnection, reference is made to postbrominated poly(4-hydroxy)styreneswhich are used in accordance with German patent application No. P 37 30784.3 as radiation-sensitive compounds in corresponding photoresists.The compounds of this invention find use as intermediates in theproduction of such polymers as poly(3,5-dimethyl-4-acetoxystyrene) andpoly(3,5-dimethyl-4-hydroxystyrene). These later compounds are useful asimproved binder resins for photoresists which have a more advantageousdissolution rate in commercially accepted photoresist developers, andare more fully described in U.S. patent application Ser. No. 07/097,815filed on even date herewith, now abandoned, and incorporated herein byreference. Alpha acetoxystyrene and beta acetoxystyrenes are describedin U.S. Pat. No. 4,144,063 and acetoxymethylstyrene is taught in U.S.Pat. No. 3,963,495. U.S. Pat. No. 4,075,237 describes1,4-dimethyl-2-hydroxystyrene, while U.S. Pat. No. 4,565,846 teaches theuse of poly(3,5-dimethyl-4-hydroxystyrene). Japanese patent No. 84023747describes anti-static compounds employing poly-acetoxymethylstyrene andU.S. Pat. No. 4,221,700 describes a stabilized synthetic polymercomposition using poly(alkylated alkenylphenol) including 2-methylparavinyl phenol. U.S. Pat. Nos. 4,600,683 and 4,543,397 describe poly(alphamethyl vinylphenol). U.S. Pat. Nos. 4,517,028; 4,460,770 and4,539,051 describe dimethyl vinyl phenol.

SUMMARY OF THE INVENTION

The invention provides as a novel compound,3,5-disubstituted-4-acetoxystyrene.

The invention also provides a process for the production of3,5-disubstituted-4-acetoxystyrene which comprises (a) acylating2,6-disubstituted phenol, for example with acetic anhydride undersuitable catalysis to provide 3,5-disubstituted-4-hydroxyacetophenone,then (b) esterifying the 3,5-disubstituted-4-hydroxyacetophenone toproduce 3,5-disubstituted 4-acetoxyacetophenone, then (c) hydrogenatingthe 3,5-disubstituted-4-acetoxyacetophenone to form1-(3',5'-disubstituted-4'-acetoxyphenyl)ethanol and then (d) dehydratingthe 1-(3',5'-disubstituted-4'-acetoxyphenyl)ethanol to form 3,5disubstituted-4-acetoxystyrene.

Each of the above 3,5-substitutions are independently C₁ to C₁₀ alkyl oralkoxy, amino or halo.

The invention further provides 3-substituted-4-hydroxy- and4-acetoxystyrene compounds having the formula ##STR2## wherein: R ishydrogen or acetyl; and

Hal is chlorine or bromine; and

R1, R2 and R3 are independently hydrogen, alkyl, alkoxy, or halogen; and

wherein R1 and R2 may combined to form a cycloaliphatic ring, consistingof 6 to 12 members; and wherein, when R is acetyl at least one of R₁, R₂and R₃ and are not hydrogen, and when R is hydrogen, at least two of R₁,R₂ and R₃ are not hydrogen.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment, the preferred 3,5-substitution is methyland the preferred embodiment will now be described in detail. The othersubstitutions are obtained analogously. In the process for theproduction of 3,5-dimethyl-4-acetoxystyrene, one begins with2,6-dimethylphenol, which is readily commercially available, andesterifies it with acetic anhydride to produce2,6-dimethyl-4-phenylacetate. Then, via a Friedel-Crafts catalysis orFries rearrangement this is converted to3,5-dimethyl-4-hydroxyacetophenone. This is then esterified with, forexample, acetic anhydride to form 3,5-dimethyl-4-acetoxyacetophenone.The latter is then hydrogenated to form1-(3',5'-dimethyl-4'-acetoxyphenyl)ethanol. This is then dehydrated withan acid to form 3,5-dimethyl-4-acetoxystyrene monomer.

A typical reaction sequence may be described schematically as follows:##STR3## In the preferred embodiment the first two reaction stepsproceed essentially simultaneously. That is, one charges the reactionvessel with 2,6-dimethylphenol, a slight excess of acetic anhydride anda Friedel-Crafts catalyst such as hydrogen fluoride. The acylation isconducted at a temperature of from about 5° C. to about 100° C., or morepreferably from about 20° C. to about 80° C. A most preferredtemperature is about 50° C. The reaction proceeds at a preferredpressure of from about 700 mm Hg to about 780 mm Hg for from about 1 toabout 5 hours. Although hydrogen fluoride is the preferred catalyst,others may be also used such as AlCl₃, H₂ SO₄, BF₃, and SnCl₄. In thealternative, the acylation may be conducted by a Fries rearrangement, ina manner well known to the skilled artisan.

Attempts to directly reduce the keto functionality in 3,5-disubstituted4-hydroxyacetophenones by means of e.g. catalytic hydrogenation orcomplex hydrides, as known to the skilled artisan, invariably lead tooverreduction with exclusive formation of 4-ethylphenol derivatives.While not wishing to be bound by theory it is believed that thisbehavior is caused by formation of quinonemethide intermediates whichare then preferentially reduced at the methide carbon as shown in thefollowing scheme: ##STR4##

This undesirable behavior can be pre-empted by preventing phenolate ionformation, which is essential to the above mechanism. This is mosteasily done by protecting the phenolic functionality, e.g. byesterification.

Esterification of the hydroxyl group for its protection is preferablyaccomplished with acetyl chloride or with acetic anhydride. However, anyreagents known to protect hydroxyl functions can be used. These includein particular the formation of ethers, such as methyl, methoxymethyl,2-methoxyethoxymethyl, methylthiomethyl, tetrahydropyranyl,cyclopropylmethyl, allyl, isopropyl, cyclohexyl, t-butyl, benzyl,o-nitrobenzyl, 9-anthrylmethyl, and 4-picolyl ethers, but also silylethers, such as trimethylsilyl and t-butyldimethylsilyl ethers, esterssuch as acetates, pivaloates, benzoates, and 9-fluorene-carboxylates,carbonates such as methyl, 2,2,2-trichloroethyl, vinyl, and benzylcarbonates, arylcarbamates, and sulfonates such as methanesulfonates andtoluenesulfonates. Protective groups of this type are described byTheodora W. Green, Protective Groups in Organic Synthesis, John Wiley &Sons, 1981. However, the acetoxy group is particularly preferred. Thereaction product 3,5-dimethyl-4-hydroxyacetophenone is thereforeesterified with a suitable acetylating agent, preferably with aceticanhydride. In this process, the 3,5-dimethyl-4-hydroxyacetophenone isrefluxed with an excess of acetic anhydride for from about 15 to about20 hours. Excess acetic anhydride as well as generated acetic acid areremoved by distillation in vacuo. This is conducted, for example at apressure of from about 15 to about 30 mm Hg and at a temperature of fromabout 15° C. to about 40° C., preferably from about 30° C. to about 35°C. The resultant 3,5-dimethyl-4-acetoxyacetophenone is then preferablyflash distilled at a pressure of from about 10 to about 40 mm Hg and ata temperature of from about 105° C. to about 125° C. and the resultantproduct appears as a colorless liquid which solidifies at roomtemperature.

The 3,5-dimethyl-4-acetoxyacetophenone is then catalyticallyhydrogenated. The reduction of the ketone function can be done withcomplex hydrides and by catalytic reduction with hydrogen. Sodiumborohydride is a preferred complex hydride. Lithium borohydride is alsopossible as well as reaction products that arise for example upondissolution of sodium borohydride or lithium borohydride in alcohols.The preferred reaction medium in reduction with complex hydrides isethanol or mixtures of organic solvents miscible with water, such asTHF/water mixtures. In the preferred embodiment, an autoclave is firstpassivated, for example first with 30% HNO₃ and then withKOH/isopropanol. It is then charged with the3,5-dimethyl-4-acetoxyacetophenone, an excess of hydrogen gas underpressure, a sufficient amount of a suitable catalyst to drive thereaction, and a suitable solvent. One preferred catalyst is Pd/C in anamount of from about 1 to about 4 percent by weight of the3,5-dimethyl-4-acetoxyacetophenone. Other suitable catalystsnon-exclusively include CaCO₃, Ni/Al, sodium borohydride and reducedmetal salts of Pt, Pd and Ni. The preferred solvent is ethanol and ispresent in an amount of from about 3 to about 5 parts by weight of the3,5-dimethyl-4-acetoxyacetophenone. The reaction proceeds at a preferredtemperature of from about 25° C. to about 40° C., a preferred hydrogengas pressure of from about 215 to about 250 mm Hg psig. The reaction isconducted for from about 1 to about 5 hours. The resultant product is1-(3',5'-dimethyl-4'-acetoxyphenyl)ethanol and has the appearance of acolorless oil after filtering off the catalyst and evaporating thesolvent. This oil is then dehydrated. Dehydration is preferablyconducted by vacuum heating the oil in the presence of a polymerizationinhibitor and a dehydrating agent. In one preferred embodiment, the1-(3',5'-dimethyl-4'-acetoxyphenyl)ethanol is mixed with a KHSO₄dehydrating agent and a t-butyl catechol polymerization inhibitor. Otheruseful dehydrating agents non-exclusively include bases, CuSO₄, CuCl₂,Mg(ClO₄)₂ and aluminum oxide. Other polymerization inhibitorsnon-exclusively include hydroquinone, tetrachloroquinone anddi-t-butyl-p-cresol. The dehydrating agent is present in an amount offrom about 0.25 to about 5.0 percent weight of the oil. Thepolymerization inhibitor is preferably present in an amount of fromabout 0.01% to about 5% based on the weight of the oil. The reactionvessel is heated to from about 160° C. to about 210° C., preferably 185°C. to about 190° C. at a pressure of from about 1.0 to about 15 mm Hg,preferably 1.5 to 2.0 mm Hg. The product is then distilled to acolorless liquid and then redistilled after the insertion of additionalpolymerization inhibitor.

When the hydroxy rather than the acetoxy compound is desired, theprotective group may then be split off to form the substituted4-hydroxystyrene analogs. Hydrolysis can be carried out by either theacid or the basic method. Candidates for hydrolysis agents are NH3,NaOH, KOH, and tetramethylammonium hydroxide as well as HCl or H2SO4.During hydrolysis, particularly acid hydrolysis, care must be taken thatthe styrene derivatives do not polymerize. A particular hydrolysismethod which prevents polymerization begins with hydrazinolysis withhydrazine hydrate, and is completed by hydrolysis with acids, inparticular with HCl. This method is particularly preferred.

The following non-limiting examples serve to illustrate the invention.

EXAMPLE 1 3,5-Dimethyl-4-acetoxystyrene

(36.6 g, 0.30 mol) of 2,6-dimethylphenol are mixed in an Hastelloy Cautoclave with 0.315 mol of acetic anhydride and 9 mols of hydrogenfluoride. The temperature is raised to 50° C. and the reaction runs for3 hours. After extraction and wash, 47.4 g of a gray to purple solidmass of 3,5-dimethyl-4-hydroxyacetophenone is obtained. This solid isthen esterified by refluxing with 4 mols of acetic anhydride for 19hours. After removal of acetic acid and acetic anhydride by vacuumdistillation the 3,5-dimethyl-4-acetoxyacetophenone is flash distilledto yield 47.7 g of a slightly yellow liquid. 0.1 mol of the3,5-dimethyl-4-acetoxyacetophenone, 1.2 g of 5% Pd/C as catalyst and 100ml ethanol are mixed in an autoclave and the autoclave is charged withhydrogen gas at a pressure of 215-220 mm Hg PSIG and the reaction is runfor about 21/2 hours at a temperature of about 25°-30° C. Additionalcatalyst is added as needed. The catalyst is then removed and theethanol evaporated to yield 21.5 g of a colorless oil which is1-(3',5'-dimethyl-4'-acetoxyphenyl)ethanol. 0.168 mol of1-(3',5'-dimethyl-4'-acetoxyphenyl)ethanol is added to a flask with 0.35g KHSO₄ and 0.5 g t-butyl catechol. The flask is heated to 185° to 190°C. at 1.5 to 2.0 mm Hg. A colorless liquid is distilled. After theaddition of 0.15 g of t-butyl catechol, and redistillation, 26.1 g of3,5- dimethyl-4-acetoxystyrene monomer is produced. The compound has aboiling point of 90°-91° C. at 0.5 mm of Hg and the yield is 81.8%.

EXAMPLE 2 3.5-Dibromo-4-acetoxyacetophenone.

15.7 g (0.2 mole) Acetylchloride is added dropwise to a stirred mixtureof 57.1 g (0.194 mole) 3,5-dibromo-4-hydroxyacetophenone, 1.67 g4-dimethylaminopyridine, and 19.6 g triethylamine in toluene at 60° C.After four hours of further reaction under the given conditions, thehydrochloride precipitated from the solution is filtered off and thetoluene solvent is distilled from the remaining solution under vacuumand the remaining product is recrystallized from a mixture ofdiisopropyl ether and activated charcoal. A yield of 93% may beachieved. The white, isolated crystals have a melting point of 114° C.

EXAMPLE 3 1-(3',5'-Dibromo-4'-acetoxyphenyl)ethanol

5 g of sodium borohydride is added in small portions to an icecooledsolution of 84 g (0.25 mole) 3,5-dibromo-4-acetoxyacetophenone intetrahydrofuran and water. The reaction is exothermic. When all thesodium borohydride has been added and after a further 30 minutes ofstirring, the reaction mixture is nearly clear. The solution is broughtto a pH of 2 with 2 g hydrochloric acid, the solution is extracted twicewith ether, and the combined organic phases are rinsed twice with water.After drying the ether solution, the solution is concentrated undervacuum. A yellow oil is produced, which in a high vacuum has a boilingpoint of 132°-139° C. at 0.002 Torr (mbar). The yield of this reactionstage after distillation is 80 g of a colorless oil.

EXAMPLE 4 3,5-Dibromo-4-acetoxystyrene

A mixture of 67.6 g (0.02 mole)1-(3',5'-dibromo-4'-acetoxyphenyl)ethanol, 0.35 g freshly melted andthen finely pulverized potassium hydrogen sulfate, and 0.5 gt-butylhydroquinone are heated at 20 Torr to 170°-190° C. The resultingproduct is distilled off (under vacuum) at a temperature of 140° to 160°C. It is taken up in ether, the ether solution is washed with Na2CO3,dried, and concentrated under vacuum. The remaining product is distilledat 0.02 mbar; the boiling point is 116° C. The isolated product, whichis a highly viscous oil or a white, waxy solid, has a melting point ofapproximately 75° C. The reaction yield is 27 g.

EXAMPLE 5 Preparation of 3,5-Dibromo-4-hydroxystyrene

10 g of 4-acetoxy-3,5-dibromostyrene are dissolved in 50 ml THF and 25ml methanol, 12 g hydrazine hydrate (80% aqueous solution) is added, andthe cloudy mixture is then converted into a clear solution by adding 3ml of water. After 40 minutes it is acidified with a semi-concentratedHCl to pH 2 and extracted twice with ether, the ether phase is washedtwice with water and dried over sodium sulfate, and the ether is removedwith a rotary evaporator at room temperature under aspirator vacuum. 8.5g of crude product remain, from which 6.45 g of white crystals (mp 74°C.) are obtained by recrystallization from petroleum ether.

EXAMPLE 6 o-Cresyl Acetate

First 235.5 g (3.3 moles) acetyl chloride then 282.8 g (2.8 moles)triethylamine are added dropwise to a mixture of 324 g (3 moles)o-cresol and 36.6 g (0.3 mole) 4-dimethylaminopyridine in 1 liter oftoluene. The mixture is then heated for 3 h at 65° C. The resultingsolid hydrochloride is separated by filtration and the organic phase iswashed twice with 1 N hydrochloric acid then with water. The solution isdried and then the solvent is recovered under vacuum. The remaining oilis distilled under vacuum. It has a boiling point of 87° C. at 12 Torr.The yield is 428.8 g.

EXAMPLE 7 4-Hydroxy-5-methylacetophenone

A total of 360 g dry AlCl₃ is added to a mixture of 300 g (2 moles)o-cresyl acetate and 1.2 liters nitrobenzene in small portions. Thereddish mixture is kept at room temperature with moisture excluded for12 h, and the mixture increasingly takes on a dark-green color. When thereaction mixture is poured into ice water, a light yellow emulsion isobtained, to which the quantity of a 10% hydrochloric acid needed tomake it clear is added. After 1 liter of ether has been added, twophases form, from which the ether phase is separated and washed with a7.5% potassium hydroxide solution. The aqueous phase is combined withthe potassium hydroxide solution, acidified, and the resulting product,after extraction with ether, drying, and recrystallization fromdiisopropyl ether, is isolated. The light-brown product has a meltingpoint of 108° to 109° C. The reaction yield is 122.8 g.

EXAMPLE 8 3-Bromo-4-hydroxy-5-methylacetophenone

110 g (0.73 mole) 4-hydroxy-5-methylacetophenone is suspended in amixture of 370 ml acetic acid (glacial) and 370 ml H2O, the mixture iscooled to 5° C., and a solution of 116.8 g or 38 ml (0.73 mole) brominein 100 ml acetic acid is added dropwise while cooling such that thetemperature does not rise above 10° C. Addition of bromine takes about 1h. After cooling for a further 2 h at room temperature, the product isfiltered off, dried, and recrystallized from acetonitrile. 150 g ofproduct with a melting point of 145°-146° C. can be isolated.

EXAMPLE 9 3-Bromo-4-acetoxy-5-methylacetophenone

52 g or 47 ml (0.66 mole) acetyl chloride are added dropwise to asolution of 140 g (0.6 mole) 3-bromo-4-hydroxy-5-methylacetophenone, 7.4g 4-dimethylaminopyridine and 60.6 g (0.6 mole) triethylamine in 500 mltoluene. The resulting reaction mixture is stirred for another 3 h at65° C. The hydrochloride formed is filtered off and the toluene phase iswashed twice with 2 N hydrochloric acid then twice with water. Afterdrying and distillation of the solvent under vacuum, 99 g of pureproduct is isolated. The white crystals have a melting point of 78°-80°C.

EXAMPLE 10 1-(3'-Bromo-4'-acetoxy-5'-methylphenyl)ethanol

99 g (0.37 mole) of 3-bromo-4-acetoxy-5-methylacetophenone is added to250 ml of tetrahydrofuran and cooled to 0° C. 20 ml water is added andthen 7 g (0.185 mole) sodium borohydride is added while cooling inportions such that the temperature does not exceed 20° C. After twohours stirring at room temperature, the reaction mixture is added to amixture consisting of 100 ml concentrated hydrochloric acid, 200 mlwater, and 250 g ice, the mixture is thoroughly stirred, and thenextracted with ether. The ether phase is washed first with a 5% sodiumcarbonate solution then with water. After distilling the solvent, 96.3 gof a viscous oil is obtained as the crude product which is thendistilled under vacuum according to Example 3 and yields 86.8 g ofproduct.

EXAMPLE 11 3-Bromo-4-acetoxy-5-methylstyrene

A mixture of 28 g 1-(3'-bromo-4'-acetoxy-5'-methylphenyl)ethanol and 0.5g freshly prepared potassium hydrogen sulfate is heated under a 20 Torrvacuum to 190°-200° C. The distillate is transferred to an ice-filledreaction vessel which contains 2 g t-butylhydroquinone. After 2 h, thedistillate is taken up in ether, the ether phases are treated with a 5%sodium carbonate solution and dried, then the solvent is distilled offunder vacuum. At 0.05 Torr, 6.8 g of an impure product is obtained at atemperature of 86° to 89° C., from which 18 g of pure monomer can beobtained.

EXAMPLE 12 (COMPARATIVE EXAMPLE) Attempted direct reduction of3,5-dibromo-4-hydroxyacetophenone

10 g of 3,5-dibromo-4-hydroxyacetophenone are dissolved in methanol,cooled to 0° C., at which point the calculated amount of sodium boronhydride is slowly added with stirring. After one minute, thin layerchromatography shows the presence of 4-ethylphenol, but not of1-(3',5'-dibromo-4'-hydroxyphenyl)ethanol (by comparison with authenticsamples). After one hour, the mixture is worked up by pouring intowater, extracting the ether, and drying on a rotary evaporator. Analysisof the products by NMR spectroscopy shows the material to be a mixtureof starting material and 4-ethylphenol, with no alcohol reductionproduct present.

Similar results are obtained with other solvents and complex hydrides aswell as with attempted catalytic hydrogenations.

EXAMPLE 13 Dehydration of 1-(3',5'-dibromo-4'-acetoxyphenyl)ethanol withcopper(II)sulfate

5 g 1-(3',5'-dibromo-4-acetoxyphenyl)ethanol are dissolved in 50 g oftoluene, to which mixture are added 0.25 g of anhydrouscopper(II)sulfate. The mixture is refluxed for 2 hours and the toluenethen removed on a rotary evaporator. A yellow oil remains which afterrecrystallization from petrol ether yields 2.9 g of3,5-dibromo-4-hydroxystyrene as white crystals, mp. 75° C.

What is claimed is:
 1. A process for the production of3,5-disubstituted-4-acetoxystyrene which comprises (a) conducting aacylation step which consists essentially of acylating 2,6-disubstitutedphenol with acetic anhydride under hydrogen fluoride catalysis at atemperature of from about 5° C. to about 100° C. at a pressure of atleast about 700 mm Hg for from about 1 to 5 hours to provide3,5-disubstituted-4-hydroxyacetophenone, then (b) esterifying the3,5-disubstituted-4-hydroxyacetophenone to produce3,5-disubstituted-4-acetoxyacetophenone, then (c) hydrogenating the3,5-disubstituted-4-acetoxyacetophenone to form1-(3',5'-disubstituted-4'-acetoxyphenyl)ethanol and then (d) dehydratingthe 1-(3',5'-disubstituted-4'-acetoxyphenyl)ethanol to form3,5-disubstituted-4-acetoxystyrene, wherein each of said3,5-substitutions are independently C₁ to C₁₀ alkyl or alkoxy, amino orhalogen.
 2. The process of claim 1 wherein step (c) is conducted by theheating under hydrogen as positive pressure in the presence of acatalyst.
 3. The process of claim 2 wherein the hydrogen gas pressure isin the range of from about 200 to about 250 PSIG.
 4. The process ofclaim 2 wherein said heating is conducted at a temperature of from about25° C. to about 40° C.
 5. The process of claim 2 wherein said catalystof step (c) is Pd/C.
 6. The process of claim 2 wherein said step (d) isconducted in the presence of a dehydrating agent and a polymerizationinhibitor.
 7. The process of claim 6, wherein said dehydrating agent isan acid.
 8. The process of claim 6 wherein said dehydrating agent isKHSO₄.
 9. The process of claim 6 wherein said polymerization inhibitoris t-butyl catechol.
 10. The process of claim 1 wherein said 3,5substitution is methyl.